In a typical electrostatographic printing machine (such as a photocopier, laser printer, facsimile machine or the like), an imaging member is employed that is exposed to an image to be printed. Exposure of the imaging member to the image to be printed records an electrostatic latent image on the imaging member corresponding to the informational areas contained within the image to be printed. Generally, the electrostatic latent image is developed by bringing a toner or developer mixture into contact therewith.
The developed toner image recorded on the imaging member may be transferred to an image receiving substrate such as paper via an intermediate transfer member. The toner image particles may be transferred by heat and/or pressure to an intermediate transfer member, or more commonly, the toner image particles may be electrostatically transferred to the intermediate transfer member by means of an electrical potential between the imaging member and the intermediate transfer member. After the toner image has been transferred to the intermediate transfer member, it is then transferred to the image receiving substrate, such as by contacting the substrate with the image on the intermediate transfer member under heat and/or pressure.
Intermediate transfer members enable high throughput at modest process speeds. In four-color systems, the intermediate transfer member also improves registration of the final color toner image. In such systems, the four component colors of cyan, yellow, magenta, and black are synchronously developed onto one or more imaging members and transferred in registration onto an intermediate member at a transfer station.
In electrostatic printing machines in which the toner image is transferred by heat and pressure from the intermediate transfer member to the image receiving substrate such as paper, it is important that the transfer of the toner particles to the image receiving substrate be as complete as possible. Less than complete transfer to the image receiving substrate results in image degradation and low resolution. Near complete transfer is particularly important when the imaging process involves generating full color images since undesirable color deterioration in the final colors can occur when the primary color images are not efficiently transferred from the intermediate transfer member.
Thus, it is important that the intermediate transfer member surface have excellent release characteristics with respect to the toner. Conventional materials known in the art for use as intermediate transfer members possess the strength and electrical conductivity necessary for use in such intermediate transfer members, but can suffer from poor release characteristics, especially with respect to higher gloss image receiving substrates.
It is also important for the production of high resolution images that the gloss of the image produced match the gloss of image receiving substrate such as paper. Paper comes in a broad range of glosses, from low to very high gloss, and it is difficult to maintain the gloss match of an image over the range of paper glosses.
U.S. Pat. No. 3,664,300 (Joseph) discloses an apparatus for treating the surface of an imaging member with a solid hydrophobic metal salt of a fatty acid by fibrous treating means. The treating means is preferable a woven or non-woven web of materials including furs, natural fibers such as cotton, wool and hair, and synthetic fibers such as nylon and cellulose derivatives.
U.S. Pat. No. 4,796,048 (Bean) discloses an apparatus which transfers a plurality of liquid images from a photoconductive member to a copy sheet utilizing an intermediate transfer belt. The intermediate transfer belt can optionally be cleaned with a brush having flexible bristles following transfer of the image to the image receiving substrate. No materials for forming the flexible bristles are disclosed.
U.S. Pat. No. 5,119,140 (Berkes et al.) discloses a single layer intermediate transfer belt preferably fabricated from clear, carbon loaded or pigmented Tedlar.RTM. (a polyvinylfluoride available from E. I. du Pont de Nemours & Co.). Following transfer of the image to a plain paper substrate, the intermediate transfer belt is cleaned by a "conventional magnetic brush roll structure".
U.S. Pat. No. 5,175,591 (Dunn et al.) discloses a cleaning brush for a photoreceptor surface comprising bristles capable of abrading the photoreceptor surface. The abrasions aid in the removal of toner particles adhering to the photoreceptor surface following transfer of the image to a substrate via an intermediate transfer device. Dunn et al. does not disclose the use of a cleaning brush for an intermediate transfer member. The bristles of the brush must be of sufficient hardness to scratch the photoreceptor surface. The bristles are preferably polypropylene. Further, Dunn et al. discloses that fibers of polytetrafluoroethylene are too soft and unsatisfactory in that they undesirably deposit polytetrafluoroethylene on the photoreceptor surface.
The need remains for a method of maintaining an intermediate transfer member's release properties throughout its useful life while also improving the matching of image gloss to substrate gloss.